1. Field of the Invention
The present invention relates to an active matrix display device having an active matrix display portion which is structure by formation of a thin film transistor (hereinafter, referred to as a TFT) over a substrate.
2. Description of the Related Art
Conventionally, display devices typified by a liquid crystal display device and a light-emitting device have been known as active matrix display devices using active elements such as TFTs. In these active matrix display devices, pixel density can be increased. In addition, the active matrix display devices are small and lightweight, and consume low power. Accordingly, products using active matrix display devices such as a monitor for a computer, a television, and a monitor for a car navigation system have been developed as one of flat panel displays in substitution for a CRT display.
In addition, each of these active matrix display devices has a structure including an active matrix substrate. For example, in a case of a liquid crystal display device, display is performed in the following manner: a substrate (an active matrix substrate) provided with a pixel portion including a first electrode (a pixel electrode) and the like in addition to a plurality of TFTs and wirings and a substrate (an opposite substrate) provided with a second electrode (an opposite electrode), a light-shielding film (a black matrix), a colored film (a color filter), and the like are attached to each other; a space between these substrates is filled and sealed with a liquid crystal material; and liquid crystal molecules are oriented by an electric field which is applied between the pixel electrode and the opposite electrode to control the amount of light from a light source.
Note that, in the active matrix substrate, the wirings (a source line, a gate line, a storage capacitor line, and the like) formed in the pixel portion are electrically connected to lead wirings (also referred to as a common line, a ground line, or a ground line) which are formed in the periphery of the pixel portion in order to secure a function and an optimum layout of the active matrix substrate. Conventionally, these lead wirings have an advantage that the manufacturing process can be simplified because the lead wirings can be manufactured in the same process with the use of the same conductive material as the component formed in the pixel portion.
However, these lead wirings are long in length and wiring resistance thereof is increased even with the use of a low-resistant metal. Therefore, as compared with the wirings of the pixel portion, it is necessary to increase the width of the lead wirings. However, in order to increase the width of the lead wirings, there has been a problem that the area of a frame portion (a peripheral region over the substrate other than the pixel portion) is increased.
In downsizing the display device, it is important to narrow a frame thereof in order to form a panel having a large display region, and various attempts have been made (for example, see Patent Document 1: Japanese Published Patent Application No. 2000-187237).